Shift of communication media from conventional copper wires to optical fiber cables has been in progress to achieve high-speed communication in the Internet and corporate networks.
In general, an optical fiber is made of silica glass or the like and is vulnerable to external force. For this reason, it is common practice to cover the periphery of the optical fiber with two protection coating layers, that is, a primary coating layer and a secondary coating layer, and thereby to protect the optical fiber from external force and an environment which may affect the characteristics of the optical fiber.
Furthermore, it is desirable that optical fibers be distinguishable from each other from the view point of work efficiency in installation and the like. However, the protection coating layers are generally clear and colorless. Thus, a colored layer as a tertiary coating layer is generally provided on the outer periphery of the secondary coating layer. An optical fiber provided with such a colored layer is referred to as a colored optical fiber.
FIG. 9 is a cross-sectional view of a three-layer structure colored optical fiber 90 in a conventional technique. The three-layer structure colored optical fiber 90 includes a glass optical fiber 101, a primary coating layer 103, an uncolored secondary coating layer 905, and a colored layer 907. The glass optical fiber 101 is made of silica glass. The primary coating layer 103, the uncolored secondary coating layer 905, and the colored layer 907 are made of ultraviolet curing resin and formed around the glass optical fiber 101 in this order. The colored layer 907 is made of an epoxy acrylate-based resin. Since the uncolored secondary coating layer 905 is not colored, the secondary coating layer 905 is clear and colorless.
Meanwhile, there is proposed a two-layer structure colored optical fiber having a structure with no colored layer. In such a colored optical fiber, the primary coating layer or the secondary coating layer is colored. Accordingly, there is no need to additionally provide the colored layer and diameter reduction of the optical fiber can be achieved. For example, Patent Document 1 discloses a colored optical fiber which includes a primary coating layer and a secondary coating layer and in which the primary coating layer is colored.
In an optical fiber cable using the colored optical fibers, easy take-out of the colored optical fibers brings about a great effect on work efficiency in operations such as installation and after-branching of the optical fiber cable.